1. Field of the Invention
This invention relates to the methods and apparatus for purifying water using a combination of electrolytic purification and introduction of microbiocidal metal species into the water. More particularly, the invention relates to the combination of electrolytic purification and the introduction of biocidal metal ions into the water.
2. Description of Related Art
Electrolytic purification of water has been carried out for some time. The process involves the purification of water that is saline, i.e., that has some concentration of halide ion in it. For instance, in many swimming pools in Australia, where electrolytic purification of pool water is currently more popular than in the United States, a slight salinity level is achieved by dissolution of quantities of sodium chloride into the pool water. The water, with its dissolved halide ion, is passed through an electrolytic cell. The halide ions are oxidized by electrolysis to form hypohalic acid, hypohalite ions, or both (believed to occur through the intermediate of molecular halogen), which have known utility in disinfecting water (and whose use is typically known as xe2x80x9cchlorinatingxe2x80x9d the water). In addition, the electrolysis reaction converts water into hydrogen and oxygen; some of the oxygen is converted further into ozone, which also has a disinfecting effect on the pool water.
Electrolytic purification is desirable because it is safe, effective, and for applications such as swimming pools, hot tubs, spas, etc., it eliminates much of the need for the pool owner or operator to handle chemicals and monitor water chemistry. The salinity levels necessary to achieve effective chlorination levels are typically well below the organoleptic thresholds in humans, and the primary chemical required to be handled by the operator is a simple alkali metal halide salt. In addition, operation of the electrolytic cell is comparatively easy, and requires little attention beyond ensuring the proper current and voltage levels are set, and maintaining the correct salinity levels in the water.
One of the disadvantages associated with electrolytic purification is the cost of the electrolytic cell, as well as the cost of replacement electrodes, which can corrode, become fouled with scale and the like or otherwise become inactivated over time. These costs are primarily driven by the size of the electrodes, which are typically constructed from titanium coated with platinum or ruthenium. Electrodes having a surface area sufficient to generate adequate chlorine levels represent a significant portion of the cost of installing and maintaining an electrolytic purification system. In addition, electrolytic cell life is limited due to the current density through the cell over time.
The introduction of microbiocidal metals into water to sanitize it has also been suggested for and used in various water purification applications, such as in pools and spas. In particular, various methods of introducing metal ions, such as silver ions or copper ions, into the water have been proposed. The use of these ions to purify, e.g., pool water, results in decreased need for chlorination. Highly chlorinated pool water is often uncomfortable to, and is thought to possibly have adverse effects on the health of, swimmers and bathers, decrease the useful life of swimwear, etc. One method of introducing such ions into water that has been proposed involves the use of sacrificial electrodes containing metals corresponding to the desired ions, including alloys of silver and copper, and electrolytically dissolving the metals into the water. Other methods include contacting the water with substrates that have been coated or impregnated with metal, soluble metal salts, or some combination thereof. These methods can be difficult for pool owners to control, and as a result, can sometimes provide unreliable control of metal delivery, and can cause stained surfaces when too much metal has been delivered, or result in insufficient sanitation when too little metal has been delivered.
This invention results from the surprising discovery that the use of electrolytic purification of water can advantageously be combined with the introduction of microbiocidal metals to provide a purification system and method that is safe, effective, and economical. The combination of microbiocidal metals with electrolytic purification allows decreased levels of metal ion to be present, along with decreased chlorine levels. As a result, there is decreased likelihood of unpleasant side effects from either technique, such as staining of pool surfaces, chlorine damage to hair and clothing of swimmers and bathers, etc. At the same time, the pool water is sanitized for a wide variety of microorganisms by the use of multiple methods. Finally, the presence of metals in the water, at least through the resulting decrease in necessary chlorine levels, can reduce the size of electrodes necessary to maintain appropriate levels of protection. This results in a substantial decrease in the cost of deploying and maintaining an electrolytic purification system.
In one embodiment, the invention relates to a method for purifying water by forming in an electrolytic cell molecular halogen, hypohalic acid, hypohalite ions, or combinations of these, from halide ions dissolved in the water; and dissolving one or more metals in the water.
In another embodiment, the invention relates to a system for purifying water, having an electrolytic cell comprising a plurality of electrodes sufficient to electrolytically convert halide ion in the water into molecular halogen, hypohalic acid, hypohalite ions, or combinations of these; and a metal generator, which provides concentrations of one or more metals to the water.
The metal generator may contain metallic material which dissolves or disperses into the water, or may contain soluble metal salts, or combinations thereof.
These embodiments of the invention result in a method and system that achieve the advantages of electrolytic purification and the advantages of microbiocidal metal ion purification, but vastly reduce the concomitant disadvantages of each. Further, the combination of techniques results in a significantly more economical purification process than is achievable with electrolytic purification alone.